The present invention relates to small internal combustion engines and, more particularly, to vapor return primers for diaphragm carburetors.
Internal combustion engines which utilize diaphragm carburetors are generally faced with a vapor lock problem. The reason that these types of carburetors are susceptible to vapor lock is that diaphragm carburetors are not vented to atmosphere as are float-type carburetors. Thus, there is a need to enable diaphragm carburetors to function without experiencing vapor lock.
Vapor lock is caused by the vaporization of fuel in the carburetor fuel path prior to the entrance of the fuel into the carburetor metering chamber. When a carburetor heats up, generally due to engine heat, causing the fuel in the carburetor to vaporize, fuel vapor and/or emulsion are present at the inlet needle of the carburetor metering chamber. As more fuel is required by the carburetor, the inlet needle opens and the fuel vapor and/or emulsion enter the metering chamber, causing vapor lock. Thus, the carburetor is starved for raw or liquid fuel, and results in lean fuel supply to the engine.
To overcome this dilemma, particularly in large internal combustion engines which utilize diaphragm carburetors such as snowmobiles, and the like, a fuel take off fitting with calibrated orifice is located at high pressure side of the carburetor fuel delivery system to "scalp" off vapor and/or emulsion and return the vapor and emulsion to the fuel tank. As the engine begins to heat up causing the fuel to vaporize in the carburetor, the vaporized fuel is "scalped" off and returned to the fuel tank to enable raw fuel to enter into the metering chamber of the carburetor. When vaporization is not occurring in the carburetor, raw fuel is still "scalped" off to the fuel tank without hampering the function of the carburetor. This is due to the fact that the carburetor fuel pump delivers fuel at such a rate that only about 20% of the fuel delivered is required for functioning of the carburetor. With these large internal combustion engines, an orifice may be calibrated that does not substantially reduce the pressure on the high pressure side of the carburetor and thus, the carburetor is enabled to function.
In small internal combustion engines like the microengines which are utilized in chain saws, weed trimmers and the like, the pressure on the high pressure side of the fuel delivery system is in the order of 2 to 6 PSI. In order to provide the carburetors of these microengines with orifices, a very, very small orifice is needed to keep the pressure on the high pressure side of the fuel delivery system from going to zero causing failure of the carburetor. Orifices which were calibrated to be used in these microengines were so small that dirt or the like in the fuel stream easily blocked the orifice, rendering the orifice inoperable. Thus, there is a need for a device which enables the scalping off of fuel in small internal combustion engines.
The present invention provides the art with a vapor return primer for small internal combustion engines (microengines). The present invention serves the dual purpose of priming a small internal combustion engine prior to starting the engine and scalping off fuel from the carburetor of the internal combustion engine during a continuous running mode to regulate pressure in the carburetor and to prevent vapor lock. The present invention enables the carburetor to run cooler and provide easier starts when the engine is hot. The present invention enables fuels such as gasahol, a gasoline alcohol mixture, to be utilized in small internal combustion engines. Since gasahol vaporizes at a lower temperature than gasoline, the present invention enables the scalping off of the vapor and/or emulsion to enable raw fuel to enter the carburetor metering chamber.
Accordingly, the vapor return primer of the present invention includes a housing having an inlet and an outlet, both to enable passage of fluid through the housing. A resilient flexible membrane is coupled with the housing. The membrane is adapted to be flexed for priming the carburetor. The membrane is flexed from a first original position to a compressed position wherein fluid is expelled from the housing. The membrane reflexes from the compressed position to its original position wherein fluid is drawn into the housing. A pressure relief mechanism is coupled with the housing to regulate pressure in the carburetor and to enable one-way flow of fluid to exit the housing. The pressure relief mechanism also enables fuel to exit the housing during flexing of the membrane and during the continuous running mode of the engine.
From the subsequent detailed description taken in conjunction with the drawings, other objects and advantages of the present invention will become apparent to those skilled in the art.